Theoretical and empirical traditions in psychology have long focused on the benefits of emotion in producing greater personal and professional effectiveness. In particular, the ability to understand the emotional states of other people is crucial for facilitating effective interactions in social life and in the workplace, providing a window into others' reactions and attributions, their inclinations and intentions, their likely future behaviors. Accuracy in perceiving emotion is a core construct within "emotional intelligence" (EQ)--defined as the "accurate appraisal and expression of emotions in oneself and others and the regulation of emotion in a way that enhances living" (Mayer, DiPaolo & Salovey, 1990, p. 772). Academics, practitioners, and the public alike have been excited about the promise of EQ, and to date the ability to recognize others' emotions has been the component of EQ most reliably validated by scientific research. Past work showed that individuals who are more accurate in reading emotion are also better employees, but has left untested the implicit mechanism of behavior: people who can understand others' emotions are able to use the information they gain in order to adjust their behavior to be more adaptive and appropriate for the particular interaction. The proposed studies are ambitious by going further and examining the specific behaviors responsible for this relationship. The large-scale multi-phase study explores what people do differently when they can or cannot understand the emotions of those around them. The particular context for the studies is negotiation, which can be a highly emotional arena for interpersonal interaction, and in which effective communication and emotional behavior can be crucial for productive outcomes. Rather than assuming that some people are always effective and others always ineffective, the study also examines the importance of emotional "match", in the extent to which interaction partners uniquely understand each others' idiosyncratic styles of expressing themselves.